A two-shaft worm machine with single-threaded treatment or worm elements is known from DE 1 180 718 A. The outer contour of the worm elements is composed of circular arcs in cross-section. The active flank located in the rotational direction has an outer contour, which is composed of three circular arcs, the centre points of which are either located on the outer radius or on the longitudinal axis of the worm elements. The drawback is that the worm elements only allow a small flexibility in the adjustment of the shear and/or extensional flows acting on the material to be processed.